5. Dual Display Channel

XFree86 releases later than 4.1.0 support dual-channel display on the ct69030.
This support can be used to give a single display image on two screen with
different refresh rates, or entirely different images on the two displays.

Dual refresh rate display can be selected with the "DualRefresh"
option described above. However to use the dual-head support is slightly
more complex. Firstly, the ct69030 chipset must be installed on a PCI bus. This
is a driver limitation that might be relaxed in the future. In addition the
device, screen and layout sections of the "XF86Config" must be
correctly configured. A sample of an incomplete "XF86Config" is
given below

The device section must include the PCI BusID. This can be found from the
log file of a working single-head installation. For instance, the line

(--) PCI:*(0:20:0) C&T 69030 rev 97, Mem @ 0xed000000/24

appears for the case above. Additionally, the "Screen" option
must appear in the device section. It should be noted that if a flat
panel is used, this it must be allocated to "Screen 0".

The server can then be started with the "+xinerama" option
as follows

startx -- +xinerama

For more information, read the Xinerama documentation.

It should be noted that the dual channel display options of the 69030
require the use of additional memory bandwidth, as each display channel
independently accesses the video memory. For this reason, the maximum
colour depth and resolution that can be supported in a dual channel mode
will be reduced compared to a single display channel mode. However, as
the driver does not prevent you from using a mode that will exceed the
memory bandwidth of the 69030, but a warning like

If you see such display corruption, and you have this warning, your choices
are to reduce the refresh rate, colour depth or resolution, or increase the
speed of the memory clock with the the "SetMClk" option described
above. Note that increasing the memory clock also has its own problems as
described above.